This invention concerns a method for manufacturing polyester fibers with good adhesion to rubber, particularly by using a spin finish containing epoxy compound, blocked isocyanate compound and polyoxyethylene amine compound. Polyester fibers, such as polyethylene terephthalate, are fibers which have superior physical and chemical properties, are produced industrially in large quantities, and are extremely useful in many fields. They are also very suitable materials for use as reinforcers of various kinds of rubber.
However, polyester fibers have a great defect in that their adhesion to rubber is inferior to polyamides such as nylon 6, nylon 66, etc., which are also representative industrial fibers.
If polyamide fibers are treated only with a resorcinol-formaldehyde-latex (RFL) adhesive, they have very good adhesion to rubber. In the case of polyester fibers, even if they are treated with RFL, good adhesion cannot be obtained.
Consequently, for some time many attempts have been made to improve the adhesion of polyester fibers and rubber. Representative methods include (1) when treating the raw cord textile by the so-called "dipping" RFL treatment, it is pretreated, before the RFL treatment, with an adhesive such as an epoxy compound, etc., or by mixing a novolak resin or an esterophilic ingredient such as 2,6-bis(2',4'-dihydroxyphenyl-methyl)-4-chlorophenol, known by the trade name of "Pexul," with the RFL and dip-treating the textile; (2) adding an adhesive such as an epoxy, isocyanate, etc. compound at the yarn stage, and then dip-treating with RFL. Although the former method does provide a certain amount of the desired adhesion, it has defects such as the fact that the amount of the adhesive used is great and the treatment method is troublesome, etc., so that the cost is increased. The latter method, although it has the practical advantage that like the polyamide fibers, the later dipping treatment can be performed with RFL alone, it has the disadvantage that the essential adhesion is somewhat unsatisfactory. Consequently, in order to increase the adhesion in the latter method, the concentration of the adhesive used in treating the yarn is markedly increased, or the heat-treating conditions are made extremely severe, etc., so that the treatment method of the yarn itself must deviate greatly from the range of practicality, which causes new problems.
Many methods of adding epoxy compounds to polyester fibers at the time of making the filaments are known, but the conventional methods all have the defects that, as mentioned above, their adhesion is not yet sufficient or they require severe treatment conditions far beyond practicality, etc., so they cannot be considered satisfactory methods. Also, many methods of adding isocyanate compounds at the time of making polyester fiber filaments have also been proposed, but these methods are also unsatisfactory from the viewpoints of adhesion or productivity. Furthermore, methods of adding both epoxy and isocyanate adhesives at the time of making polyester fiber filaments are also known, but although these methods are somewhat better from the viewpoint of adhesion than the cases in which epoxy compounds or isocyanate compounds are added separately, they have nevertheless not been able to reach a satisfactory level of performance with the existing technology.
Thus, as shown by the fact that many patents exist for methods of adding epoxy and isocyanate compounds alone, the development of methods for adding these adhesives effectively has been a prominent technological problem, and it may be easily inferred by anyone in the industry that good adhesion cannot be simply and easily obtained merely by adding these adhesives one by one.